Effects of Opsonin Density and type on the Phagocytosis of Beads

When a pathogen enters the body, the immune system releases small proteins that opsonize the foreign entity. This serves as a signal to macrophages to engulf the pathogen, a process known as phagocytosis. Depending on the type of opsonin covering the invasive species, phagocytosis can occur in structurally different ways. My research aimed to examine how different opsonin types and densities affect phagocytosis both qualitatively and quantitatively. Microspheres were used to replicate pathogens, and IgG antibody alongside iC3b complement were the opsonins studied. First, a Dose-Response curve was made to show it was possible to cover the bead with different amounts of opsonin, i.e. change the density of antibody or complement on the bead surface. Then, the distinctly opsonized beads were fed to cells and the effectiveness of phagocytosis was analyzed using two different techniques: time-lapse movies and 3D image reconstruction. Through the former method, it was quantitatively found that more densely opsonized beads were more effectively phagocytosed, and that cells transitioned through phagocytosis quicker with IgG covered beads. This may suggest that the actin dynamics and cytoskeleton remodeling occur faster through the IgG signaling pathway than through that of iC3b. Progress was made through the 3D image reconstruction to better observe the phagocytic cup structure formed by the cell and to more efficiently note a difference between iC3b and IgG consumption in a qualitative sense. Phagocytic studies can supply useful information for drug treatments involving passage of the drug through the cell membrane to reach its activation site. My research showed that opsonin density and type affect phagocytosis tremendously.